龙首山南麓新发现的地震地表破裂带——兼论1954年山丹M_(S)71/4地震发震构造  

Discovery of the surface rupture zone along the southern branch of the Longshoushan Fault Zone,NW China and its significance to the deep structures of the 1954 Shandan M_(S)71/4 earthquake

作　　者：赵迪 陈鹏[2] 李荣西[1] 吴小力[1] 赵帮胜 刘齐 王晓雪 ZHAO Di;CHEN Peng;LI Rongxi;WU Xiaoli;ZHAO Bangsheng;LIU Qi;WANG Xiaoxue(School of Earth Science and Resources,Chang’an University,Xi’an 710061,Shaanxi,China;Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China)

机构地区：[1]长安大学地球科学与资源学院,陕西西安710061 [2]中国地质科学院地质力学研究所,北京100081

出　　处：《地质力学学报》2022年第4期501-512,共12页Journal of Geomechanics

基　　金：第二次青藏科考项目(2019QZKK0704);中国地质科学院地质力学研究所基本科研业务费(DZLXJK202107)。

摘　　要：基于详细的遥感解译和野外调查,发现龙首山南缘断裂发育有较新的地震地表破裂遗迹,包括断层坎、地震鼓包、河道的系统位错等断层地貌标志,破裂带总长度超过20 km,沿断裂走向其垂向位移介于0.35~4 m,水平位移介于0.3~1.9 m,龙首山南缘断裂主体表现为逆冲性质,仅在西端表现为局部左旋走滑的性质。通过剖面和探槽揭示,龙首山南麓地区全新世以来发生多次断层活动,最新的一次在约3.96 ka以来。经过与区域内的强震记录比对,认为此次新发现的地震地表破裂带可能是1954年山丹M_(S)71/4地震所致。1954年山丹M_(S)71/4地震在浅表沿两条断裂同时发生了地表破裂,表现为正花状构造的变形样式。这种同震位移分配现象以往多发现于走滑型地震中,此次在逆冲型地震中发现。龙首山南缘断裂地表破裂带的发现为揭示1954年山丹地震的震源过程和破裂样式提供了新的证据和思路。A detailed field-based remote sensing interpretation in this study revealed abundant recent seismic surface ruptures on the southern margin of the Longshoushan Fault,including fault scarps,mole tracks and displacements of river channels.The total length of the surface rupture zone is over 20 km.The most recent vertical and horizontal displacements of the late Quaternary geomorphic markers fall into the range of 0.35~4 m and 0.3~1.9 m,respectively.The southern Longshoushan Fault is a high-angle thrust fault,and it only exhibits left-lateral strike-slip on the west end.Revealed by profile and trench along the surface rupture,the southern branch of the Longshoushan Fault Zone has gone through several earthquake events since the Holocene,and the latest one happened around 3.96 ka.By comparing with the strongest earthquake recorded in this region,it is suggested that the 1954 M_(S)71/4Shandan earthquake may have caused the newly discovered surface ruptures,which developed along both the southern and northern branches of the Longshoushan fault zone,presenting a positive flower structure at the shallow surface.This coseismic displacement distribution mostly is found in strike-slip earthquakes in previous studies,but it is found in a thrust earthquake this time.The discovery of coseismic surface rupture on the southern branch of the Longshoushan Fault Zone will throw light on the focal mechanism and rupture pattern of the 1954 Shandan M_(S)71/4earthquake.

关 键 词：青藏高原东北缘 1954山丹M_(S)71/4地震 龙首山断裂带 同震地表破裂 花状构造 

分 类 号：P54[天文地球—构造地质学] P65[天文地球—地质学]